The present invention relates to methods for compacting articles made of powder material by means of powder compacting presses, provided with a reciprocable ram disposed above the press die supporting bed. More specifically, the invention relates to an improved method for compacting powder material by a combination of a mechanical toggle mechanism and fluid operated mechanism for actuating the ram of a press.
The present invention is an improvement on the powder compacting method practiced by the press disclosed in U.S. Pat. No. 3,826,599, assigned to the same assignee as the present invention. The press disclosed in the aforesaid patent is provided with a ram disposed above the press bed in which is mounted a powder compacting apparatus comprising a die plate having one or a plurality of die cavities disposed therein. A punch is reciprocably disposed in each die bore and is actuated by the drive mechanism of the press by means, for example, of a power-driven camshaft and appropriate cam followers driving the punch holder. A ram is reciprocably disposed above the press bed, therefore above the die plate, and is reciprocated in timed relationship with the reciprocation of the punch holder by an appropriate cam, cam follower, lever and toggle mechanism. A set of punches, each adapted to cooperate with a punch disposed in a die bore, can be mounted on the end of the ram and, or in addition, the ram, in its fully extended position, may be used to clamp over the die plate an anvil adapted to close the die cavity or cavities, and having a face overlapping the die cavity opening or openings, against which the powder material disposed in the die cavities is compacted by the punch or punches held in the die bore or bores. The anvil, together with a powder material dispenser and a finished part pick-up mechanism, is mounted on the end of a positioning arm, such as to be arcuately or linearly displaced and positioned over the die cavities in timed relationship with the die cavity filling step, the compacting step and the finished article ejection step. Such an arrangement of elements is described in the aforesaid patent and in U.S. Pat. Nos. 3,561,054 and 3,574,892, for example, of common ownership herewith.
The present invention results from an improvement on the ram operating toggle mechanism of U.S. Pat. No. 3,826,599, as disclosed in U.S. Pat. No. 4,166,716, consisting in providing a floating fluid pressure displaceable anchoring and pivoting point for the ram toggle mechanism, such that the ram may additionally be longitudinally displaced as a result of the reciprocation of the anchoring and pivoting point. Adjustable limit abutments are provided for the fluid actuated reciprocating anchoring and pivot point of the toggle mechanism, such that the stroke provided by the fluid actuated mechanism may be precisely determined, together with the extreme positions of the reciprocating member.
The results achieved by the present invention are the direct benefits from an arrangement for compound reciprocation of a press ram and for precisely determining the extreme dwell positions of the ram. By thus providing a compound stroke of the press ram, part of the stroke being mechanically effected by a toggle mechanism and part of the stroke being pneumatically or hydraulically effected, the motion increments being either consecutive or simultaneous, according to the appropriate timing of the beginning and end of the two separately controlled motions, diverse results can be achieved by the present invention.
One such result is that, in arrangements where the end of the ram is provided with a clamping mechanism for the positioner anvil, by proper timing of the clamping step pneumatic or hydraulic pressure may be exerted on the anvil prior to final mechanical clamping provided by the toggle mechanism, so that the clamping pressure applied on the anvil may be more progressive and is effected with a cushioning effect.
Another result is that, in structures comprising punches mounted on the end of the ram, such punches being adapted to penetrate into the die cavities and compact the material therein in the die bore between the end face of the ram mounted punches and the end face of opposedly reciprocating punches disposed in the die bore, compacting of the powder material can be effected in a more progressive manner as compared to methods using a mechanically actuated upper punch, and the density of the finished part is greatly improved as compared to the density of parts compacted under more conventional methods. When compacting certain powder materials, either due to their composition or due to the binder used to bind the particles of powder together, after filling of the die cavity and when the lower punches are advanced in the die bores the frictional effect of the die bore wall on the powder and the tendency of the powder material to stick to the die bore wall cause a pre-compacting of the powder material at progressive levels from the level in engagement with the lower punch compacting face throughout the mass of the powder material. This results in a greater density of the finished part at the levels closer to the compacting face of the lower punch than at levels farther removed from the lower punch compacting face. When the part is compacted between opposite punches, and the upper punch is held stationary during compacting, or an anvil overlapping the die cavity is used, the density of the finished part, when using that type of sticky powder material, is greater proximate its lower surface than it is at the core or at the upper surface of the finished part. The present invention permits, by proper timing of the pneumatic or hydraulic ram motion relative to the ram motion caused by the mechanical toggle mechanism, to tailor with precision the amount of motion and the pressure exerted by the upper punches during their reciprocation, either contemporaneously with the reciprocation of the lower punches or subsequently thereto, such that during displacement of the upper punches, while maintaining the lower punches stationary, for example, the density of the finished part proximate its upper surface is greatly increased, thus forming a finished article having a more constant density throughout its thickness.